Heterogeneous Voltage Dependence of Inward Rectifier Currents in Spiral Ganglion Neurons

Zun-Li Mo and Robin L. Davis Department Biological Sciences, Rutgers University, Piscataway, New Jersey 08855-1059 Mo, Zun-Li and Robin L. Davis. Heterogeneous voltage dependence of inward rectifier currents in spiral ganglion neurons. J. Neurophysiol. 78: 3019-3027, 1997. Inward rectification was characterized in neonatal spiral ganglion neurons maintained in tissue culture. Whole cell current and voltage-clamp techniques were used to show that the hyperpolarization-activated cationic ( I h ) current underlies most or all of the inward rectification demonstrated in these neurons. The average reversal potential ( 41.3 mV) and cesium sensitivity were typical of that found in other neurons and cell types. What was unique about the hyperpolarization-activated currents, however, was that the half-maximal voltages ( V 1/2 ) and slope factors ( k ) that characterized I h current activation were graded from neuron to neuron. Voltage-clamp recordings made with standard bath and pipette solutions revealed V 1/2 values that ranged from 78.1 to 122.1 mV, with slope factors from 7.6 to 13.1. These gradations in the voltage-dependent features of the I h current did not result from variability in the recording conditions because independently measured Na + current-to-voltage relationships were found to be uniform (peak current at 20 mV). Moreover, the range and average V 1/2 and slope values could be altered with activators [8-(4-chlorophenylthio) adenosine 3 ,5 -cyclic monophosphate in combination with okadaic acid] or inhibitors { N -[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide}of protein indicating that I h current heterogeneity most likely resulted from differential phosphorylation.